Adding Panels to a 12v RV

socko12345

I have an old Airstream with 2 Kyocera KD135 135W 17.7v panels and a Morningstar ProStar 30amp controller connected to 12v batteries. I dry camp (no hookups) from October till April each year in western Colorado, Utah, and northern Arizona. For a variety of reasons, my panels must be mounted directly/flat to the roof of the trailer and cannot be tipped---wind storms, lack of roof access, etc.

On a typical Colorado cloudy day in December/January, my ProStar registers no more than 5 or 6 amps for just a few hours! I'd like to raise that to at least 12 or 14amps. Note: On sunny days in Sedona, I can easily get 12 to 14amps, so I feel confident that my systems is efficient in terms of wire/installation---it's the combination of weather, latitude, and flat-mounted panels that's reducing my amperage.

I'd like to add additional panels and/or a MPPT. I have a budget of $1000-2000. For remaining roof space, I have a 6' x 8' and a 4' x 8' space, so I have lots of options.

The Kyocera KD-315 is the cheapest $/W from Wind & Sun, but its a 39.8V panel. If I buy that panel, how should I connect my current panels? Or are there other panels that work work better with my current setup?

What would you do?

vtmaps

Re: Adding Panels to a 12v RV

socko12345 wrote: »

The Kyocera KD-315 is the cheapest $/W from Wind & Sun, but its a 39.8V panel. If I buy that panel, how should I connect my current panels? Or are there other panels that work work better with my current setup?

Welcome to the forum. You will need an MPPT controller to take advantage of those panels. For a 12 volt system you want the panels configured in parallel. You will need a combiner box with a circuit breaker for each panel.

A problem that many RVs face is partial shading (even an overhead power line or an antenna from your rig) or variable panel orientations (curved roof). If all the panels are not identical or the panels do not have identical exposure, the MPPT can be a bit confused as to where the max power point is.

--vtMaps

socko12345

Re: Adding Panels to a 12v RV

Currently, the panels are in a parallel configuration with a combiner box and circuit breaker/panel.

I typically don't have any overhead obstructions or shading: the only things on my roof are vents, and the panels are higher. Also, the panels are also mounted flat on a roof-rack, so they have identical exposure. And there are no powerlines, trees, buildings, etc. in the desert.

Still, I do occasionally encounter overhead shadows from things (like trees and powerlines). In the case of shadows, would a MPPT be worse than my current ProStar? Or just loose its MPPT benefits over a standard charge controller?

Overall, what would be your personal choice on how to increase power?

Cariboocoot

Re: Adding Panels to a 12v RV

The KD140 panels are electrically so close to the 135's that they are interchangeable for all practical purposes. You could add them in any sort of configuration that suits: two more in parallel on the existing controller for instance. They do cost more per Watt, but they are easier to handle (lighter weight and smaller area). http://www.solar-electric.com/kykd140wa12v1.html

Spending several hundred $ on an MPPT controller probably is not warranted in this case. It won't gain you much with the panels you've got and isn't needed for adding more panels unless you go with the higher Vmp type.

niel

Re: Adding Panels to a 12v RV

you may also benefit from having a few of the pvs like coot mentioned remote mounted on the ground rather than on the rv roof. this way you have extra pvs when you need them and you can aim them in the desired direction being they aren't on the rv roof. you would have to remember to put them away if you leave though. you could still put 2 140w 12v pvs in parallel on the roof with the current ones and do remember to fuse each of them before combining to go to the controller. btw, more than 2 more pvs could far exceed the capacity of your present controller so stick with 1 or 2 more like these or see if you can find one of the higher power 12v evergreen pvs that may still be floating around as around 200+w from 1 of these would work out well.

socko12345

Re: Adding Panels to a 12v RV

Firstly, thanks vtmaps, Cariboocoot, and niel for your advice and opinions! I truly appreciate both your time and experience.

In terms of adding 2 140W panels, (and thus doubling my current supply), I am concerned that my sub-par solar production days would only be doubled from 5amps to 10amps. If I'm charging a phone, listening to the radio, and my small electric cooler kicks on, I'm using about 5amps; charge the laptop, and I'm at 8. So if I double my panels and my amps double (from 5 on a bad day) to 10, I am left with vary little to charge the batteries---> only 2 to 5amps.

I do think that placing a panel on the ground is an option for some people (and I've definitely seen it done), but for security and protection from wind storms, I'd like to keep the panels secured on the roof. Micro bursts can easily blow over 80mph!

If I can't make the 135W panels work with other higher voltage panels, I am willing to sell them (and the ProStar), and buy 2 315W Kyocera's and a MPPT. If I understand MPPT, they seem ideal for my cloudy, cold, windy winter days plus my need to charge cold batteries.

It is also worth mentioning, that the Airstream is heated solely by a woodburning stove, so inside temperatures are typically around 20F or 30F in the morning when I wake up. Since the batteries sit on the floor, in a dark, vented box, they stay pretty cold. Thus, having a MPPT combined with two 39.8V panels, seems like an effective way to reach the higher required voltages for charging the cold batteries.

Unless I'm overlooking another possibility, it seems I have two basic options:

spend $700 on two KD140W panels (and wires, circuit breakers, mounts, etc). which still might not be enough power

--or--

sell the panels/controller that I own and spend $1300 on two KD315W panels and a TriStar 60, a system which could easily be transferred to a small cabin in future years

Cariboocoot

Re: Adding Panels to a 12v RV

socko12345 wrote: »

If I can't make the 135W panels work with other higher voltage panels, I am willing to sell them (and the ProStar), and buy 2 315W Kyocera's and a MPPT. If I understand MPPT, they seem ideal for my cloudy, cold, windy winter days plus my need to charge cold batteries.

Ah, not quite. Nothing makes power from cloudy days. The power just isn't there. The cold temps may up the Voltage from the panels, but that does not always equate to charging power. The biggest advantage from MPPT is the ability to run "any array to any system" so to speak; the flexibility in adapting array Voltage to system Voltage. The cold weather factor can actual work against you if it causes your array Voc to exceed the controller's input max (a problem that always has to be considered up here in the Great White North).

It is also worth mentioning, that the Airstream is heated solely by a woodburning stove, so inside temperatures are typically around 20F or 30F in the morning when I wake up. Since the batteries sit on the floor, in a dark, vented box, they stay pretty cold. Thus, having a MPPT combined with two 39.8V panels, seems like an effective way to reach the higher required voltages for charging the cold batteries.

Your batteries may not be as cold as you think. With current going in or out they rarely attain ambient temperature. On the other hand, having a good charge controller with a remote temp sensor will alleviate much of the problem if they do get too cool or hot.

The thing about panels is that they are a current source, and that's what is needed for charging. Being able to supply sufficient Voltage is easy; supplying it at a practical current level is a tad more difficult.

Unless I'm overlooking another possibility, it seems I have two basic options:

spend $700 on two KD140W panels (and wires, circuit breakers, mounts, etc). which still might not be enough power

--or--

sell the panels/controller that I own and spend $1300 on two KD315W panels and a TriStar 60, a system which could easily be transferred to a small cabin in future years

Pretty much it: add on to the existing or completely change the whole thing.
Two of the 140's would double your output to 10 Amps on a bad day. That would be 1/3 of their potential.
Two 315's operating at the same 1/3 capacity on an MPPT controller would be around 13 Amps in my estimation.
Is it worth spending double the money for 3 more Amps?

CATraveler

Re: Adding Panels to a 12v RV

Not sure what batteries you have - 2 12V starting/marine batteries?

Have you considered larger batteries? The discharge rate would be less and you could have the capacity for several cloudy days.

Cariboocoot

Re: Adding Panels to a 12v RV

With 14 Amps maximum current as the system is, more battery capacity could make it worse rather than better. A couple of Marine/RV batteries are probably around 180 Amp hours (if this is what the OP has) so it would work well with the panels he's got on good days. Doubling the panels so that there's 10 Amps on bad days should be a good solution for that size battery bank. If he went up to 220 Amp hours then the 14 Amps he's got now would have trouble with it and adding panels would only correct the new problem, not make the old one go away. Basically it's hard to get power out of panels when the sun doesn't shine.

CATraveler is absolutely right, though; the battery bank size will make a big difference in the performance of any system.

Endurance

Re: Adding Panels to a 12v RV

If you move your trailer often enough, you might benefit from a 12vdc to 12vdc converter connected to a switched power source on your tow vehicle. If you're driving very far, it will be one more source of power for little cost.

niel

Re: Adding Panels to a 12v RV

if things are that tight and you need all that you can get then an mppt cc would be good to get in addition to more pvs as it could squeak a bit more out of the pvs by maximizing on the best power point. this often equates to about 10% on average and if you are getting 5a now it would only translate to another 1/2a. this is only working with the available solar power and nothing can really make up power from a reduction in insolation for when the sun isn't there then neither is the power. mppt only works with what is presented to it and would be an expensive endevour for you to utilize, but maybe that extra current is worth it to you.

as to the ground mounts blowing away, i would hope that you would anchor them or weigh them down as a side precaution on the possibility of such a weather occurrence happening. you would do this for a tent or an awning coming off of the rv and often there would be the good option of laying the pvs flat on their face in a pinch. all in all, having remote mounted pvs would give you more net power than the many pvs you'd need to have on the rv, if you had that much room on it to do that, and would cost far less to you for the realized power. it's your money and your call.

socko12345

Re: Adding Panels to a 12v RV

Right now, my system is useless. Why? Because after mid-November, even with no loads, the batteries still won't reach a Float charge*. Thus, I have no reservations in spending more money to get something that will actually charge the two batteries (~250aH in total).

For me, there really isn't anyway around a permanent, flat, roof-mount for the panels. So I must expect and calculate for a maximum of 30% efficiency. I'm sure there are folks that would never accept that much loss, but I can live with it. My work has me on the road from April through November/December, so I don't own or rent a home. I live in the Airstream full-time during the off-season.

Spending $1000-$2000 for the opportunity to camp for free on BLM land, seems well within reason. But my current system doesn't work at all; it's a complete loss.

I think I'll sell the panels and charge controller, and invest in at least a 750W system. If my projected new system (say, 3 255W panels) can easily get my battery bank up to a Float charge, I'll probably look into a newer, large bank. Right now, I need to get my solar production sorted out. Once I know I'm not going to have any charging problems, I'll recycle my current battery bank, and get a nice, fresh, bank.

I'll let you guys know how it goes....

many Thanks!

*this is in western Colorado; once I head south to Arizona, I have plenty of power

niel

Re: Adding Panels to a 12v RV

well i hope it works out for you. do let us know the changes you try and the results. the real problem is the fact you have the pvs laying flat on the roof for any real winter production and that's also providing you keep it clear of snow too.

socko12345

Re: Adding Panels to a 12v RV

Update

Short story: I spent a lot of money to use my vacuum cleaner.

Longer story: I bought 3 255w panels from Northern Arizona Wind & Sun, a TriStar 60 MPPT, a Mini DC Plus breaker box, and a ton of heavy gauge copper wire. While I waited for all the parts to come in, I built a rack to hold my two 135w panels on the side of the airstream.

The rack works pretty well. I've seen a little over 15amps, during the month of December 2012 while in Moab and Sedona. Of course, it's design is contingent upon good weather (sub ~15mph wind), campground space, and southern orientation, but over all I really like it. I can remove the panels for towing and security, and collapse the whole lot in the event of a wind storm.

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I've redone nearly all the electricals in the camper, too. The MidNite MNDC175 Plus (Mini DC breaker box Plus with 175amp inverter breaker) has really helped me to streamline my system. I replaced the Romex DC feed lines to the Airstream's fuse box with 6awg wire (protected with a 20a breaker) and switched to 2/0awg wire from the batteries to the inverter (175a breaker). The IOTA 55a battery charger, ProStar 30, and the TriStar 60 are all wired to their own breaker, 80a, 30a, and 80a, respectively, which is in the MNDC175 Plus. The 80a breakers for the TriStar60 and the IOTA 55 are both panel mounts; originally, I thought I would need another enclosure for the 80a panel mounts, but the MNDC Plus has room for the panel mount breakers as well as for 4 DIN rail breakers, and my 175a inverter breaker. Fitting all the wiring in the enclosure wasn't easy, but do-able.

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Previously, I was using 6awg wire from the batteries to the inverter; with the 2/0awg I can give my 1000w Xantrex ProSign inverter enough power to run my small shop-vac---which is needed around our dog and mt. bikes.

Another beneficial change was rewiring my batteries. I have two 12v batteries wired in parallel, but I didn't connect the line/load wires to opposite terminals/batteries; I had connected the main wires to the first batteries, and then ran leaders to the other battery. Now, I have both batteries connected with leaders, and then the neg feed wire is on one battery and the pos feed wire is on the second battery. Being wired properly, I'm able to get more amp/hours and shorter charge times from my bank. At some point, I'll replace the trashed "learner" batteries with nicer ones, but that's an expense for another year. For now, we're enjoying being able to charge the batteries and basically unlimited power when its sunny!

On the note of batteries, my order from NA W&S included a Trimetric meter, so now I know exactly how many amp/hours I'm using: about 50/night. That's with lights, 12v cooler, cooking_vent_hood, laptop, cell phone chargers, and watching DVD's. Not bad. I think a bank of 200 to 250 amp/hours would work very well for us.

I've installed 2 of the 255w panels with one remaining. The panels are ~30v and 8a. I'm in Sedona now, and the last week has been partly cloudy (cirrus or altostratus? clouds)... anyways, very typical cloud weather for the winter in Colorado, Utah, and northern Arizona. With the two panels and the MPPT, I've been getting 20--30amps! Adding in my 10 to 15 from the two 135W panels, and I'm doing very well. (The two 135w panels use a ProStar30 and are wired in parallel to the 255w panels which use the MPPT.)

My blown-out battery bank doesn't hold much more than 100amp/hours (although its rated for 180), so I'm still fairly screwed if there's a really cloudy day (such as a rainy or snowy day), but the solar panels, wiring, and charge-controllers are working better than I ever thought possible.

socko12345

Re: Adding Panels to a 12v RV

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I'm pretty much done. I have to secure a few of the 255w panels' wires to the roof, but everything is connected and I'm currently converting sunlight into heavy metal. Rad!

Despite the lack of sunlight---both due to clouds and length of day, 5 days past the winter solstice---my batteries are sitting at 14.9v. I'm hoping the batteries will make it to a "Float" charge soon, but the forecast for tomorrow calls for rain. At any rate, I'm confident that with nearly 1kW of potential power, my battery bank is now the weakest link.

FYI, the battery bank consists of one Napa RV/Marine battery (100a/hr rating) and one Batteries Plus "deep cycle" (80a/hr rating). Not only have both batteries been run through the ringer, both sucked from day 1...

inetdog

Re: Adding Panels to a 12v RV

socko12345 wrote: »

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Congratulation on your new power consuming lifestyle! Everybody seems to confirm that your power usage will always grow to match the size for your system. :-)
I like your "solar awning".
Am I correct that at this time you have all 5 panels connected in parallel into your MPPT controller? Or do you have a single series string?
More info on the Vmp and Imp figures for the two types of panels would be helpful.

socko12345

Re: Adding Panels to a 12v RV

I'm sure we'll be using more power than before: previously, we didn't even have enough power to run the cooler, much less lights at night.

The three 255w Solar World Panels (I think they're 31v and 8a max) are run in parallel to the MPPT. The two 135w Kyocera's (I think 18v and 7.5a) are run in parallel to the ProStar.

Shadowcatcher

Re: Adding Panels to a 12v RV

One thing to bare in mind is that conservation needs to be part of the equation i.e. the use of LED lights the other aspect is knowing the goesinta and goesouta by monitoring the battery(s) depth of discharge. Recommended a Trimetric or Victron battery monitor. Also a good set of battery cables will allow you to put some charge in your battery from the tow vehicle.

BB.

Re: Adding Panels to a 12v RV

I could not tell for sure--But do you have something that prevents winds from taking the panel through its range of motion when deployed at an angle?

Also--I would probably suggest cones/tape around the boundry--and/or a bit of foam to protect on corners, sharp/hard edges, etc. against those not paying attention (ouch).

-Bill

kellylipp

Re: Adding Panels to a 12v RV

Very nice looking system! Ditto on the eliminate the headache points!

Kelly

niel

Re: Adding Panels to a 12v RV

good deal on the system. hope the pvs hold up during travel and do let us know if you encounter any problems there.

by my calculations you may wish to get a bigger capacity battery bank as in the worst weather and season you are getting upwards of 45a from the pvs. this will certainly rise much higher at times. i figure possibly around 66a with some inefficiencies accounted for. we recommend a range of between 5% and 13% and is 900ah to 346ah at the 45a charge. for the 66a i figure it could be this would be 1320ah to 508ah. this is far more than you are probably figuring on, but you can get agm type batteries such as the sunxtenders from concorde that can take a higher charge when presented to the battery and will not gas when properly charged. maybe a pair of pvx1290t batteries would work out well for you. any higher in capacity and i believe you'll need freight shipping.

in the case of paralleling batteries please use extra heavy wires of equal lengths to tie them together. this helps to keep inequalities between the batteries at a minimum and will certainly allow better operation of handling large loads when they are presented. do be aware the voltage of the batteries will sag with very high loads and if you see this happening with newer batteries then you may wish to add more capacity with the same wires and keeping them all the same lengths. for more than 2 batteries (frowned upon because of inequalities setting up) do use a heavy bus bar. of course fusing/circuit breakers are always needed so be sure you have some near the batteries in case of any accidents on the wires and equipment.